As shown in FIG. 1, a human ear 10 includes an ear canal 12 which leads to the sensory organs (not shown). The pinna 11, the part of the ear outside the head, includes the concha 14, the hollow next to the ear canal 12, defined in part by the tragus 16 and anti-tragus 18. An earphone is generally designed to be worn over the pinna, in the concha, or in the ear canal.
During high pressure and high volume displacement events, air pressure can build up in the earphone and degrade sound quality. For example, certain high pressure and high volume displacement events (e.g., when an earphone is inserted or removed or repositioned in a user's ear) can cause a perceptible squeal or other sound distortion. The distortion may vary from person to person, as differences in head sizes, ear shapes and ear sizes result in variation in the response and output of the earphones across users. One approach to mitigate these issues is to include a pressure equalization port that serves to relieve air pressure that could build up within the earphone.